I install them all except AAX that way I know they're there.
They can be shared by other software later, and not all software can use the vst2 or 3, or 64x, so you cover more bases for when the ball might be hit later.
But that's just me.
In Sonar, Melodyne runs differently, so you don't need the ReWire, but it won't hurt to be there.
Like Grem said, just install them in the proper folders.
The installer will guide you where if you're unsure, and install all the VSTs, or just the 64x versions.
Edit: and when you go to use the plugins, they will say which versions are 32 or not, and they'll be organized by type.